Apparatus for the preparation and treatment of thin layers

ABSTRACT

A device for the production and treatment of thin layers on objects by means of electric gas discharges within an evacuable container comprising a coolable or heatable coaxial carrier tube mounted within a cooled double walled hollow cylinder, an object carrier arranged slidable and fixable on said carrier tube, means for maintaining an electric gas discharge, means for the production of a magnetic field within the container and means to induce treatment and cooling media into the container.

1973 F. GRASENICK 3,736,246

APPARATUS FOR THE PREPARATION AND TREATMENT O1" THIN LAYERS Filed NOV-4, 1971 2 Sheets-Sheet 1 O2 F/G. 28

1: I I I '3 F. GRASENICK May 29 1973 APPARATUS FOR THE PREPARATION ANDTREATMENT OF THIN LAYERS 2 Sheets-Sheet 2 Filed Nov. 4. 1971 1 o w n u oo o u u n u& %n u u n u n& vwv owowowowonvno ononouono o o o n o 0000000000 0 0 0 0 0 United States Patent O U.S. Cl. 204-298 7 Claims ABSTRACTOF THE DISCLOSURE A device for the production and treatment of thinlayers on objects by means of electric gas discharges within anevacuable container comprising a coolable or heatable coaxial carriertube mounted within a cooled doublewalled hollow cylinder, an objectcarrier arranged slidable and fixable on said carrier tube, means formaintaining an electric gas discharge, means for the production of amagnetic field within the container and means to induce treatment andcooling media into the container.

This application is a continuation in part of application Ser. No.778,908, filed Oct. 25, 1968, and now abandoned, which in turn is acontinuation in part of application Ser. No. 481,556, filed Aug. 23,1965, now abandoned.

The invention relates to a device for the production and treatment ofthin layers on articles by means of electric gas discharges at lowpressures. It is the purpose of this device to permit not only theapplication of coatings to a supporting element but also the reductionof the thickness of existing layers to the required level.

The provision of thin layers is of paramount and ever increasingimportance in many scientific and engineering fields, particularly forthe treatment of microscopic and ultramicroscopic preparations. Forexample, thin layers are required for the coating of optical systems,for the manufacture of high-ohmic resistors, interference filters andmicro circuits. Another example is the metallization of nonconductorsfor the purpose of obtaining electrically conductive surfaces. It isfrequently also necessary to apply thin layers of a specific thicknessand particular properties to wires.

With known devices of this kind, thin layers or coatings can be producedby vaporization in a high vacuum. Other conventional apparatuses areused for the production of quality as is obtainable by vaporization inhigh vacuum at pressures varying from 1O to 10 torr.

In general, pure or defined layers are desired. These can be attainedmore readily where contamination from the residual gas atmosphere isreduced by an appropriate improvement of the vacuum. For high-vacuumdeposition, equipment for working pressures varying from 10' to torr isavailable nowadays at reasonable cost. For still lower pressures, theexpense involved increases considerably so as to be warrantable inexceptional instances only.

Where depositions are made from the gas phase by means of electronradiation or by resorting to Penningtype discharges (where electronsproduced between the cathode and the anode are subject to the action ofa magnetic field for the purpose of extending the path of the electronsand increasing the impact rate) operated practically at any low pressureas required, it is not sufficient for pressure to be reduced inconventional vacuum plants, since residual gases (includingobjectionable, complex and varying emissions of gas by the container,attachments, sealing means, as well as back diffusion from pumps) areobviously also ionized and thus co-operate increasingly at the formationof layers.

If, however, any of the conventional apparatus is used for this purpose,which have been designed to meet the requirements of modern ultrahighvacuum techniques (including the use of special materials and sealingmeans as well as the heatability of the high-vacuum sector), theadvantages to be derived from discharge depositions are lost and thecost increases as compared with high-vacuum vaporization.

Another drawback of the Penning discharge as used in conjunction withconventional equipment is the fact that the articles are subject to highloads when, as generally required, deposition is to be made on theanode, with the cooling of the article leading to increased depositionlayers by means of resistance heating, cathode sputtering or byelectrolytic deposition of the layer-forming material on the supportingelement to be coated. In connection with other devices, electron impactvaporization is resorted to for the production of thin layers.

The properties of layers produced in conventional devices depend to alarge extent upon the process used on the one hand, and upon generallycomplex operating conditions which are difiicult to control.Consequently, the production of high-grade layers of great purity,uniform quality and thickness by means of conventional apparatus isbeset with considerable difliculties and the cost of the necessaryequipment is generally well above the economically bearable level.

Deposition of layer-forming materials from the gas phase under theaction of electric discharges is resorted to in exceptional cases only,although in recent years use has been made of the possibility ofcarrying out gas discharges at low pressures. Ordinary electricdischarges 7O (glow-discharges) up to a pressure range of approximately10f? torr seldpm produce layers, of the same high of impurities from thegas phase.

It is the purpose of the invention to provide an improved device for theproduction and treatment of thin layers on articles by means of electricgas discharges at low pressure in such a manner as to avoid theshortcomings of conventional apparatuses, as hereabove described.

According to another feature of the invention the device permits thecost-saving production of thin layers of exactly specified properties bythe deposition of one or several components (pure elements, compounds,mixed and alternating layers) from the gas phase.

Finally, the device according to the invention serves to produce layersof particular purity and of a homogeneous quality, with layer formationto be made possible also on sensitive carriers. A further object of theinvention is the provision of a device of the type hereabove described,of simple design, easy operation and featuring ready interchangeabilityof the articles to be treated.

According to the invention, such a device comprises an evacuablecontainer with inlets and outlets for the various agents enclosing adouble-walled hollow cylinder containing a cooling medium, a treatmentchamber defined by the inner walls of the said hollow cylinder, acarrier tube arranged in coaxial relation to the hollow cylinder withinlets and outlets for the cooling and/or heating media, at least oneobject carrier operated as an anode, slidably mounted on the carriertube and attached thereto by means of an elastic clamping means, acathode located in the treatment chamber and a magnet coil surroundingthe said container for the production of a DC. or A.C. magnetic field.With such a device the treatment chamber inside which the layer-formingmaterial is deposited from the gas phase or wherein the discharge burns,is subject to particular conditions permitting the application of avariety of layersalso on temperature-sensitive carriers and carrierswith a high vapor pressure. By means of the design of the deviceaccording to the invention it is possible to eliminate all residualgases from the discharge chamber which are liable to ionization duringthe discharge and likely to produce undefined conditions during theapplication and/ or removal of layers.

The attachments installed in the container for cooling purposes can beused for reducing the temperatures of such articles as are sensitive toheat or subject to high vapor pressures to a very low level without thedeposition of objectionable precipitates from the residual gases of thevacuum chamber. On the other hand, it is possible, according to theinvention, to have the article heated occasionally if and when required,and/or to increase the temperature in the chamber surrounding the objectwhen and as required if the object to which the thin layer is to beapplied, is heat-resisting.

For example, pure carbon layers can be obtained from hydrocarbons bymeans of the device according to the invention, as well as from siliconor silicon dioxide layers, depending on whether oxygen is eliminated ornot. With conventional equipment it had not been possible to obtainsilicon layers by discharges. Furthermore, it is possible to producefrom gas mixtures or appropriate compounds solid deposits of mixedlayers and compounds.

With the device according to the invention it is also possible toproduce pure layers consisting of elements, of compounds, or of mixturesof elements or mixtures of compounds, as well as mixtures of elementsand compounds, by anode sputtering depending on the type of cathode andthe gas used for sputtering. [in addition to these possibilities ofproducing thin layers by deposition from gases by cathode sputtering itis also possible to obtain thin layers by the process of additionallythinning thin laminae or deep-frozen preparations (of a biologicalnature, for example) both by chemical removal by means of activatedgases and by cathode sputtering.

The shortcomings of cathode sputtering in conjunction with normal glowdischarges result from the high gas pressure and the large proportion ofobjectionable admixtures in the residual gas. In addition to the heatingof the cathode, heavy granulation also occurs, leading to a reduction ofthe sputtering rate and producing a preparation full of fissures, ifcathode sputtering is to be resorted to for the purpose of reducing thethickness of a layer. However, cooling of the preparation makes senseonly where, as with the device according to the invention, theenvironment is deep-frozen. If the Penning discharge process isemployed, it is possible, to operate at low pressures while avoiding theproduction of impurities. The arrangement according to the inventionfinally permits uniform removal of the cathode if in addition to aconvenient electrode arrangement, an alternating magnetic field is used.The magnetic field, the cooling chamber and the electrodes all havedouble functions. On the one hand, they permit discharges at lowpressures, thereby ensuring uniform layer deposition and removal. Forlayer deposition, the object carrier in the center is operated as acathode. For microscopic structure tests where the first etching andimpression are preferably carried out without interrupting the vacuum,the object carrier is alternately operated as a cathode or as an anode.

According to a preferred embodiment of the invention, the hollowcylinder is divided into two sections in coaxial relation to each otherand interconnected by means of lead wires, the treatment chamber properextending in the area between the two sections of the hollow cylinder.As a result, precipitation of the gases introduced directly from the gasphase into the working chamber for the purpose of depositing the layer,is avoided, since this would lead to increased gas consumption.

According to an embodiment of the invention, the hollow cylinder can beprovided with a coolant feed pipe embodiment of the invention it is alsopossible to design the hollow cylinder as a Dewar vessel.

According to another feature of the invention, bathe sheets are providedin transverse relation to the axis of the hollow cylinder for thepurpose of directing diffusing gases to the cooling surfaces.

For particularly convenient operation of the device according to theinvention, the object carrier is a hollow cylindrical body comprisingtwo segments symmetrical in relation to a longitudinal central plane ofthe hollow cylindrical body, with holders for the objects to be treatedmounted on its outer surface, closed helical springs encompassing thehollow cylindrical body along its periphery. This design greatlyfacilitates the insertion and re moval of objects and provides anextremely simple attachment of the object carrier to the coolable and/orheatable carrier tube, by simply sliding the object carrier on to thecarrier tube and pressing the two segments of the object carrier uponthe carrier tube by means of the helical springs, thereby facilitatingheat exchange between the carrier tube and the object carrier. As aresult, both the object carrier and the preparations attached theretowill readily assume the treatment temperature desired.

However, it is also possible to design the object carrier as astepped-down hollow-cylindrical body comprising two segments symmetricalin relation to a longitudinal central plane of the body andprovided atone extremity with an annular flange on the outer front face of whichholders for the objects to be treated are mounted. All of these objectcarriers are preferably made from heatable materials of high thermalconductivity.

Further details of the device according to the invention will becomeapparent from the following description of several embodiments of theinvention with reference to the accompanying drawings, wherein FIG. 1shows one variant of the device according to the invention,

FIGS. 2,. 3 and 4 each represent an object carrier for the deviceaccording to the invention, and

FIGS. 5 through 8 each show a variant of the device, for the productionand treatment of thin layers according to the invention.

The device illustrated in FIG. 1 comprises an evacuable tubularcontainer 2, made of glass, for example, inside which a double-walledhollow cylinder 1 is arranged in coaxial relation to the longitudinalaxis of the container. The said hollow cylinder can be supplied with acoolant, such as liquid nitrogen, through a pipe 3 extending through theshell of the container. The cooling medium is recirculated from thehollow cylinder 1 through a pipe 3 also extending through the shell ofthe container 2. It is possible to replace the hollow cylinder 1 by atubular spiral additionally provided with close-fitting thin sheets madeof material of high thermal conductivty.

The container 2 is closed at one end 4 by means of a. plug 5 ofinsulating material, into which'a' tube 7 closed at its free extremity 6is inserted in such a manner as to protrude axially into the container 2and extending over almost its entire length. Into the tube 7 an insertpipe 8 protrudes, through which a cooling medium can be admitted to theinterior of tube 7. In special instances it is also possible to use theinsert pipe 8 for the heating of tube 7.

For that purpose, the plug 5 is provided with pipe connections 9 and/ or10 communicating with the interior and a coolant return pipe, butaccording to yet another of the pipe 8 or tube 7, respectively. Otherpotential heating means are a resistance heating system, an incorporatedheating coil or an air heater. If made of glass, the cooling cylinder 1and/ or the tube 7 can be provided with a heating winding which fordeep-freezing may be left in the cooling medium. The temperature rangefrom minus 200 centigrade up to a few hundred degrees centigrade,generally applicable for tests by means of an electron microscope, iseasily controllable. The centralized arangement permits cooling of thepreparation to be treated down to the temperature of the surroundingcooled cylinder 1 without contamination.

A longitudinally sliable object carrier 11 is provided on the tube 7. Asshown in FIG. 3, this object carrier comprises two semi-annular segments12 and 13. Two closed annular volute springs 14 encompass the objectcarrier 11 close to its extremities and press the insides of its twosegments 12 and 13 against the outer surface of tube 7. Thus the objectcarrier 11 is attached to the tube 7 on the one hand, and positivethermal contact between the tube 7 and the object carrier 11 made ofsome material of high thermal conductivity is assured on the other hand.

Experience has shown cooling of the tube 7, if it covers the entirelength of the cylinder, alone to suffice for keeping the center of thecontainer 2, that is, the working space of the device, free fromhydrocarbons and water vapors. In order to obtain appropriatetemperatures depending on the kind of work or test to be performed,independently for the preparation 15 mounted on the object carrier 11,and to avoid contamination during the insertion, it is advisable to havethe hollow cylinder 1 deepfrozen.

The preparations 15 can be either clamped to the outer surface 16 of theobject carrier 11 by means of holders 17 as illustrated in particular,in FIG. 3, or, as appears from FIG.2, they can be attached to the frontend of a stepped-down hollow-cylindrical object carrier 18, alsocomprising two segments and having at one extremity a flange 19 withradial recesses 20. In these excesses 20, holders for the variousobjects are provided, which can be attached to the object holder bymeans of countersunk radial clamping screws 21.

FIG. 4 shows another variant of the object carrier, designated byreference number 22, where the preparation 23, attached to the outersurface of the object carrier 22 are fixed by means of clamping jaws 24.

Both the preparations 15 and/or 23 proper and their means of attachmentshould not be freely exposed anywhere on their surface. For that reason,the clamping screws 21 are of the countersunk type. Likewise,preparations used in electron microscopy should be mounted on the objectcarrier in a countersunk manner.

Where a layer is to be formed from the gas phase, as illustrated in FIG.1, the object carrier 11 is operated as an anode via a connecting line25 emerging from the container 2, and surrounded by a grid 27 operatedas a cathode via a connecting line 26. If a layer is to be formed bymeans of the cathode sputtering method, the operation is inverted. Thegrid cathode 27 directly adjoins the inner surface of the coolingcylinder 1. Even where as different from this variant, a grid cathode ofa smaller diameter is used, it is advisable to provide aninterchangeablesheet adjoining the cooling cylinder 1, so as to keep the walls of thecooling cylinder always clean.

The container .2 is surrounded by a coil 28 for the production of amagnetic DC. or A.C. field in the area of the object carrier 11 and itsenvironment.

On the side opposite the plug 5, the container 2 has an aperture 29 forthe connection of a vacuum pump (not shown), by means of which, thecontainer 2 can be subjected to such low pressures as is required forthe treatment. The gas used for deposition from the gas phase isadmitted to the container 2 through a pipe connection 30 provided at thefront end 4 of the said container.

For the production of a thin layer on the preparations 15, these aremounted on the object carrier 11 which is then slid on the tube 7 andconnected to the connecting line 25. The tube 7 together with the objectcarrier 11 is inserted in the container 2, with the plug 5 tightlyclosing the aperture provided at the front end 4. After the gas feedpipe (not shown) has been connected to the pipe connection 30, and thecoolant pipes 3, 3' to a cooling system, the container 2 is evacuated bymeans of a vacuum pump connected to the aperture 29 until such time,when the required underpressure prevails.

Depending on the type of preparation to be treated, a cooling or heatingmedium is introduced through the pipe connections '9 and 10 into theinterior of tube 7. By the connection of the coil 28 a magnetic D10. orAC. field is produced in the working space of the container 2 and anelectric discharge is induced between the anode formed by the objectcarrier 11 and the grid cathode 27. On the anode, the layer materialdeposited from the gas phase is precipitated in such a manner that apure, homogeneous layer is formed on the surface of the preparations 15.

The process is terminated as soon as the layer on the preparations 15presents the required thickness. If the preparations are to be coatedwith a plurality of layers of different compositions, the processhereabove described is repeated with the appropriate feed stock.

In order to ensure the production of faultless layers, the ratio betweenthe length and the diameter of the container 2 should be chosen in sucha manner that the gas molecules are made to impinge repeatedly prior toreaching the center of the Working space. The larger the diameter, thegreater should be the length of the chamber. In order to avoid the needfor an excessive length of the cylinder 1, it is possible to insertbafile sheets directing the gas particles towards the cooled surfaces ofthe device.

In this way it is possible for the majority of water vapors andhydrocarbons contained in all vacuum ap paratuses to be eliminated fromthe reaction chamber proper. Gases of difiicult condensation, such asoxygen, nitrogen or methane, can be eliminated in a very simple manner,except where helium is used as a cooling medium, provided the dischargeitself is made to produce a barrier. The middle portion of the cylinderis closed against carrier losses as a working chamber of approximatelyone third of the entire length by means of grid-shaped electrodesperpendicular to the cylinder axis. These electrodes are negativelycharged. The adjoining cylinder spaces are either operated collectivelyor separately as a Penning discharge. Such an arrangement is illustratedin FIG. 5. The container 2 comprises two double-walled cooling cylindersections 31 and 32 interconnected by means of pipes 33. In between theworking chamber 34 proper is located. The magnet coil either extendsover the entire length of the cooling cylinders 31, 32 as shown in thedrawing, or is made of two parts. The outer discharges are electricallyoperated in the same sense. On one side, bafile sheets 35 are provided.The inner working chamber 34 is defined by limiting eltcarode 36 and 37.Furthermore, a grid 38 is provided in the working chamber 34 to be usedas an auxiliary electrode and surrounding the two object carriers 19 and11 with the preparations 15. The two-piece object carrier 11 ispositively pressed against the central carrier tube 7 by means ofhelical springs 14. The cathode is designated by reference number 39 andthe anode by 40. The gaps between the doublewalled cylinders 31 and 32and the limiting electrode 37 are designated by reference number 41, thecoolant feed pipe leading to the cylinders by 42, and the gas feed pipeleading to the working chamber by 43.

The cooling cylinder 31, 32 is of the split type because the gasesintroduced for the layer formation from the gas phase are liable tocondense on the cooling walls and to cause an objectionably high amountof gas consumption. For that purpose, in the variant shown in FIG. 5,the working chamber 34 is defined by the thin cylindrical limitingelectrode 34. This electrode protrudes only slightly into the twocylinders 31 and 32, leaving a narrow gap 41. This arrangement producesconsiderable thermal insulation in the vacuum. A similar eifect isobtained by the provision of a sheet metal cylinder inserted in athrough cooling cylinder without adjoining the same directly. Thetwo-piece cooling cylinder 31, 32 offers the advantage of permitting itstransformation into a closed cooling cylinder simply by providing anadjacent intermediate metal sheet, leaving the central space, however,clear for the provision of inserts or feed pipes.

In spite of this arrangement, objectionable gases from the remainingvacuum are admitted to the working chamber '34 through the limitingcylinders only and are precipitated when the cylinder is cooled and adischarge is in progress. Already as a result of the considerable lengthof the free path of the gas particles the gap 41 has an arresting elfecton the passage of gas. Therefore, a higher or lower working pressure canbe maintained in the Working chamber 34 than in the other portions ofthe apparatus, by the control of the gas admission directly to theworking chamber and by limiting sheets which may be slidable androtatable.

FIG. 6 illustrates yet another embodiment of the invention, particularlysuitable for the treatment of solid specimen 44 of the type occurring inmetallography, for example. In this case, no special holders for thespecimen are provided and it is also possible to treat a plurality ofspecimen at the same time.

The container 2 of this device is also surrounded by a magnet coil 28.Inside the container a double-walled cylindrical cooling vessel 45 isprovided, which surrounds the gas discharge chamber proper. Instead ofthis cooling vessel 45 a cooling coil could be used. Inside the coolingvessel 45 a pair of electrodes 47, 48 is provided. The electrode 48operated as an anode is disk-shaped and carries the specimen 44. Theelectrode 47 operated as a cathode is in the shape of a bell which isopen in the direction of the anode. Between the electrodes 47 and 48 agas discharge can be ignited in the usual manner at an underpressurevarying from approximately torr up to several millimeters. If the magnetcoil 28 is connected, the discharge can be maintained as far as therequired low pressures in the magnetic field produced by the coil.

The devices required for the cooling of the specimen, if necessary,which have been omitted from FIG. 6 so as to provide greater clarity,can be of a similar design as the cooling tube assembly 7 shown in FIG.5. Another cooling facility for the specimen, also not shown in thedrawings, consists in a cooling vessel 45 which, similar to the typeillustrated in FIG. 5, is composed of two pieces, a cooling bridge, suchas a cooling bar, being inserted in the gap between the two pieces ofthe cooling vessel, the inner extremity of the said bar being in contactwith the specimen carrier 44 formed by the anode.

Through the feed pipe 43 defined gases to be used for the performance ofthe gas discharge, are delivered in measured quantities to the dischargechamber 46 proper between the two electrodes 47 and 48. This produces aslightly higher pressure in the discharge chamber 46 than prevails inthe other chambers of the container 2, so that objectionable gases orvapors, unless held clear of the cooled walls of the device, are pushedback by the reac tion gas expanding in the vacuum.

According to the arrangement illustrated in FIG. 7 the container 2 issurrounded by two magnet coils 28 to be operated either collectively orindividually, as the case may be. The preparation 44 and the treatmentchamber 46 proper are again surrounded by a cylindrical cooling vessel49 connected to a cooling system in a manner not shown in the drawing.The preparation 44 is mounted on a heatable or coolable specimen carrier19 as shown in FIG. 2, fixed on a carrier tube 7 serving for the supplyand recirculation of a cooling or heating medium. It is possible toarrange a plurality of preparations for simultaneous treatment on thecarrier 19. This embodiment of the invention again offers thepossibility of installing a heating coil remaining in the cooling mediumin the tube 7.

In the device shown in FIG. 7, the preparation 44 can be treated bymeans of ions or electrons extracted from a Penning discharge to beignited between the electrodes designated by and respectively.

By means of a discharge a neutral plasma is produced 8 consisting ofelectrons and ions in equal proportions. Depending on the charge of thespecimen carirer 19 and/or the suction electrode 50, it is possible todirect electrons or ions to the preparation 44 and to accelerate them asrequired. For cathode sputtering ions are used, whereas electrons areemployed for the transformation of organic preparations by dehydrationinto a carbon structure which is morphologically equivalent.

For example, one of the two magnet coils 28 can be used as anelectromagnetic lens, the focal length of which is determined by theamperage applied to the magnet coil The electrodes of the Penningdischarge are designed in such a manner that although the electrons andions are allowed to occur in the direction of the specimen 44 as far asthey are attracted by appropriately choosing the potential of theelectrode 50, yet losses from charge carriers in other directions arepractically avoided. Besides, the shape of the electrodes is such as tomake it possible to vaporize the preparation 44 through the free spacein the area of the longitudinal center axis of the container 2, withinthe positive electrodes either simultaneously or at different timesdirectly .from the shuttle 51.

It is also possible to enlarge the device shown in FIG. 7 by theincorporation of additional electrodes (not shown) surrounding thepreparation 44 in such a manner that the preparation can be treated bymeans of discharges as described in connection with FIGS. 1, 5 and 6.

In the embodiment of the invention shown in FIG. 8, the wall of thecontainer 52 itself constitutes a coolable surface surrounding thepreparation 54 mounted on a carrier 53. The temperature of the specimencarrier 53 can be regulated, for example, by the admission of aliquified gas into the tube 7 holding the carrier 53 or by having gasesof different predetermined temperatures flow through the said tube.

The specimen 54 is surrounded by the anode 55 and located inside thefield of a magnet 56 whose pole pieces surround the container 53. Themagnet coil 28 of the magnet 56 is provided for the purpose of allowingthe gas discharge as hereabove explained, to be operated as a Penningdischarge.

The whole assembly is accommodated in a Dewar vessel 57 whose charge 58consists of liquid nitrogen as a cooling medium, for example.

The apparatus shown in FIG. 8 will be used preferably in such instanceswhere an object 54 is to be eroded [from both sides simultaneously, asin that case the charged particles are allowed to act upon the specimen54 from both sides at the same time. This method is used, for example,for purposes of electron microscopy.

As materials for the component parts of the apparatuses hereabovedescribed and illustrated in the drawings, glass and stainless steelhave shown to be particularly satisfactory. Commercial glasses nowadayspermit heating up to several hundred degrees centigrade and resistsudden changes of temperature very Well. The sealings of the conductorsleading to the cooling chambers allow the passage of liquid nitrogenwithout any preliminary cooling."

By means of the device according to the invention it is therefore,possible to produce thin layers on carriers by the action of electronrays depending on the depth of their penetration. The alteration oforganic substances by means of electron rays may be cited as an example.Electron rays are known to. cause progressive conversion into carbon.The accelerating voltage applied should be such as to cause penetrationof electrons, depending on the required thickness of the layers. Forthin layers, the accelerating voltage varies between a few hundred up toa thousand volts.

However, where oxygen and hydrocarbons are available in such quantitiesas are common in conventional treatment equipment, either layers areeroded or polymers produced haphazard. For example, only with a devicedesigned according to the invention is it possible to achieve conversioninto carbon in such a manner as to maintain the original structure to alarge extent as is required for purposes of electron microscopy.Superficial etching may be a first step in this direction althoughoperating conditions must again be strictly defined.

A particularly important application of this invention consists in thecontinuous and absolutely uniform coating of wires with layers ofspecific materials in the required thickness without any material loss,which had formerly not been possible.

I claim:

1. A device for the production and treatment of thin layers on objectsby means of electric gas discharges at low pressure, comprising anevacuable container, inlets and outlets for the treatment media on thesaid container, a double-walled hollow cylinder located in the saidcontainer and containing a cooling medium, a treatment chamber definedby the inner walls of the said hollow cylinder, a carrier tube installedin the said hollow cylinder in coaxial relation to same, inlets andoutlets on the said carrier tube for the passage of cooling and heatingmedia through the carrier tube, at least one specimen carrier operatedas an anode and arranged on the said carrier tube in slidable connectionwith same, spring means on the said specimen carrier for the purpose ofclamping the same to the said carrier tube, a cathode installed in thesaid treatment chamber, and a magnet coil surrounding the said containerand producing a magnetic field in same.

2. A device according to claim 1, wherein the said hollow cylinder isdivided into two conductively interconnected segments in coaxialrelation to each other, the said treatment chamber extending in the areabetween the said two segments of the hollow cylinder.

3. A device according to claim 1, wherein at least one coolant feed pipeand one coolant recirculating pipe are provided on the said hollowcylinder.

4. A device according to claim 1, wherein the said hollow cylinder isdesigned as a Dewar vessel.

5. A device according to claim 1, wherein baffle sheets are provided intransverse relation to the axis of the said hollow cylinder for thepurpose of directing diffusing gases to the cooling sunfaces.

6. A device according to claim 1, wherein a hollow cylindrical bodydefines the said specimen carrier and consists of two segments which aresymmetrical in relation to a longitudinal central plane of the hollowcylindrical body, holders for the objects to be treated being providedon the outer surface of the said hollow cylindrical body, closed annularhelical springs forming the said spring means and encompassing the saidhollow cylindrical body along its circumference.

7. A device according to claim 1, comprising a steppeddown hollowcylindrical body defining the said specimen carrier and consisting oftwo segments which are symmetrical in relation to a longitudinal centralplane of the said body, an annular flange at one extremity of the saidbody, holders for the objects to be treated mounted on the outer frontend of the said annular flange.

References Cited UNITED STATES PATENTS 2,189,580 2/ 1940 Hewlett 204-2983,100,272 8/1963 Wehner 204-298 3,310,424 3/1967 Wehner et al. 204-1923,337,438 8/1967 Gobeli et a1. 204-164 3,341,442 9/1967 Kay 204-192 JOHNH. MACK, Primary Examiner T. TUFARIELLO, Assistant Examiner US. Cl. X.R.204-164, 192

